Improved fuel injection systems allow internal combustion engines to increase fuel economy, reduce noxious emissions such as NOx and particulate matter, and increase power. Some of these gains come through increasing pressures of the fuel prior to injection into a combustion chamber. Increased pressures allow for more complete atomization of the fuel to increase the surface area of the fuel. The increased surface area promotes fuller combustion. Increasing the pressure of the fuel at the combustion chamber is accomplished in a number of manners including hydraulic intensification as shown in U.S. Pat. No. 6,305,358 issued to Lukich on 23 Oct. 2001. An alternative system uses an improved fuel pump to deliver high pressure fuel to a common fuel rail as shown in U.S. Pat. No. 5,497,750 issued to Mueller et al on 12 Mar. 1996. In both systems, timing of a fuel injection event may determined by electronic control of a valve such as movement of a solenoid.
However, providing a directly operated check valve or DOC valve provides an additional benefit of more controllability of the fuel injection system.
With a DOC valve, the fuel pressure as well as timing may be varied to create a fuel injection rate shape. By controlling the delivery of hydraulic fluid to a cavity over a check valve, a valve opening pressure needed to open the check valve may be varied. This increased controllability allows the fuel injection system to further lower engine noise and reduce emissions. Fuel from the common rail may also be used in a similar manner.
Control of DOC valve generally requires precise machining including numerous passages machined or cast into an injector body. Improved controllability typically involves using multiple control valves. The additional machining and control valves increase costs of the fuel injection system. Further, multiple control valves may increase actual size of a fuel injector reducing space on a cylinder head of an engine for other needed hardware.
The present invention is directed to overcoming one or more of the problems as set forth above.